The purpose of the studies is to isolate, identify and characterize Delta6-lithocholenic acid (Delta6-LC) as a significant metabolite of chenodeoxycholic acid (cheno) in man. Specifically, the project has the following aims: (1) To isolate Delta6-LC both in vitro in fecal incubations and in vivo in the colon as a bacterial metabolite of cheno. The 14c and 2H2 labeled precursor will be used and the metabolites analyzed by thin-layer chromatography (TLC), gas-liquid chromatography (GLC), mass spectrometry (MS) and nuclear magnetic resonance. (2) To study the hepatic biotransformations and the intestinal absorption of 14-C- and 2H2-Delta Delta6-LC in vivo. After i.v. injection & small intestin infusion of the compounds, duodenal bile will be collected and the metabolites identified by TLC, GLC and M.S. (3) To study the colonic bacterial biotransformation of 14C- and 2H2-Delta6-LC in vitro and in vivo. These studies also encompass in vitro isotope dilution studies in which trace amounts of 14C- Delta6-LC are incubated in a fecal medium with unlabeled cheno in order to determine the role of Delta 6-LC as an intermediate in the epimerization of cheno to urso. The biotransformation products are analyzed by TLC, GLC and M.S. The importance and health-relatedness of the studies are evidenced by preliminary findings by the P.I. which indicate Delta6-LC to occur as a significant intestinal bacterial metabolite of cheno. The studies will (a) enhance the understanding of the metabolism of cheno which represents a physiologically important bile acid in man, and (b) provide the basis for a comprehensive exploration of the physiological as well as potentially toxic effects of cheno and its metabolites during their enterohepatic circulation.